1. Field of the Invention
The present invention relates to a novel graft copolymer, a process for producing the copolymer and a resin composition containing the copolymer. More particularly, it pertains to a novel graft copolymer having syndiotactic polystyrene chain as the graft component which copolymer is excellent in heat resistance, chemical resistance, electrical properties, moldability, etc., favorable in toughness, tensile strength, tensile elongation, tensile modulus of elasticity and compatibility and also useful as a raw material for composite materials, heat resistant elastomer and the like; a process for efficiently producing the aforesaid copolymer; and a resin composition comprising the aforementioned copolymer as the principal component which composition is endowed with compatibility, adhesivity, impact resistance and well balanced physical properties.
2. Description of the Related Arts
As styrenic polymers, there are generally known a styrenic polymer produced by radical polymerization the stereostruction of which is of atactic configuration and a styrenic polymer obtained by the use of a Ziegler series catalyst the stereostructure of which is also of atactic configuration.
Heretofore, styrenic polymers produced by the radical polymerization method have been molded to various shapes by various molding methods and widely used as domestic electrical appliances, office machines, household goods, packaging containers, toys, furnitures, synthetic papers and other industrial materials. Because of their atactic configuration in stereochemical structure, however, such styrenic polymers have suffered the disadvantages of inferior heat resistance and chemical resistance.
Under such circumstances, in order to solve the above-mentioned disadvantages of the styrenic polymers having atactic configuration, the group of the present inventors succeeded in the development of the styrenic polymers having a high degree of syndiotactic configuration, and further a syndiotactic styrenic polymer formed by copolymerizing a styrene monomer with the other component. (refer to Japanese Patent Application Laid-Open Nos. 104818/1987, 187708/1987 and 241009/1988).
The above-developed syndiotactic polymer or copolymer is excellent in heat resistance, chemical resistance, electrical properties, moldability, etc., and is expected to find new applications in a variety of fields.
However, the aforesaid styrenic polymer, especially the syndiotactic polystyrene (SPS) is not sufficient in toughness, elongation, impact resistance, compatibility with other type of resin and is almost devoid of adhesivity to a metal, thereby inevitably restricting the scope of application.
As a means for improving such drawback, there is proposed a method in which an .alpha.-olefin is grafted onto SPS, which method however, still suffers the disadvantage that the grafted copolymer can not sufficiently be developed to an elastomer, since the method fails to form a structure wherein the soft segment consisting of the .alpha.-olefin chain is placed between the hard segments consisting of styrene chain.
On the other hand, an attempt is made to employ the divinylbenzene residue of the polymer main chain as the graft reaction initiation point (refer to Japanese Patent Laid-Open Application Nos. 118510/1989 and 123811/1989), but nothing is known so far about the actual example of the copolymer formed by grafting the olefinic graft precursor onto SPS. Examples of the known copolymer with SPS include an olefin/SPS copolymer and an unsaturated carboxylic acid ester/SPS and the like (refer to Japanese Patent Application Laid-Open No. 7705/1991).
Although a highly crystalline copolymer is obtained by the aforesaid process in the case of a low content of the monomer, a high content thereof results in the formation of an amorphous polymer, thus failing to make full use of the mechanical, thermal and chemical characteristics of SPS. The aforesaid process, therefore, suffers the disadvantage that the amount of the copolymerizable monomer is limited for the purpose of maintaining a high degree of syndiotacticity, which makes it impossible to obtain in a wide range the materials having the characteristics of SPS by compounding therein with other thermoplastic resin or a filler.
The use of a resin compatibilizer as the third component is taken into consideration, but an appropriate resin compatibilizer can not be found because of the high molding temperature of SPS and further, the use thereof unfavorably causes the possibility of bringing about the deterioration of the resin composition to be produced.
Under such circumstances, intensive research and investigation were made by the present inventors for the purpose of developing and providing a SPS-based graft copolymer having SPS chain grafted thereonto, which copolymer maintains the inherent characteristics of SPS excellent in heat resistance, chemical resistance, electrical properties, moldability, etc., and is improved in toughness, tensile strength, tensile elongation, tensile modulus of elasticity and compatibility with an olefinic resin and a diene resin and the like, thereby making itself useful as a raw material for composite materials and heat resistant elastomers.
As a result, it has been found by the present inventors that the above-mentioned purpose is attained by the copolymer formed by copolymerizing a styrenic monomer in a specific proportion with a high polymer having polymerizable carbon-carbon double bonds in the side chain thereof and having a high degree of syndiotactic configuration with regard to the stereoregularity of its styrenic chain as well as a reduced viscosity and a melt index each in a prescribed range; the aforementioned copolymer is easily obtained by grafting a styrenic monomer onto a high polymer having polymerizable carbon-carbon double bond in the side chain thereof; and a resin composition comprising the aforesaid graft copolymer as the principal component can also achieve the purpose. The present invention has been accomplished on the basis of the above-mentioned finding and information.